It is well known in the separation art that certain crystalline aluminosilicates can be used to separate one hydrocarbon type from another hydrocarbon type. The separation of normal paraffins from branched chain paraffins, for example, can be accomplished by using a type A zeolite which has pore openings from 3 to about 5 Angstroms. Such a separation process is disclosed in U.S. Pat. Nos. 2,985,589 to Broughton et al. and 3,201,491 to Stine. These adsorbents allow a separation based on the physical size differences in the molecules by allowing the smaller or normal hydrocarbons to be passed into the cavities within the zeolitic adsorbent, while excluding the larger or branched chain molecules.
In addition to being used in processes for separating hydrocarbon types, adsorbents comprising type X or Y zeolites have also been employed in processes to separate individual hydrocarbon isomers. In the processes described, for example, in U.S. Pat. Nos. 3,626,020 to Neuzil, 3,663,638 to Neuzil, 3,665,046 to de Rosset, 3,668,266 to Chen et al., 3,686,343 to Bearden Jr. et al., 3,700,744 to Berger et al., 3,734,974 to Neuzil, 3,894,109 to Rosback, 3,997,620 to Neuzil and B426,274 to Hedge, particular zeolitic adsorbents are used to separate the para isomer of bi-alkyl substituted monocyclic aromatics from the other isomers, particularly para-xylene from other xylene isomers. U.S. Pat. No. 3,707,550 to Stine et al. mentions (as one possibility among a very large group), a silver or silver/potassium exchanged X-zeolite for use in the separation of C.sub.8 aromatic isomers, but only following the removal of the ortho-xylene in a "separation zone" by means which appear to be conventional distillation.
In U.S. Pat. No. 4,376,226 to Rosenfeld et al. the separation of the ortho aromatic isomer from a mixture of aromatic isomers is disclosed using CSZ-1 as a crystalline aluminosilicate adsorbent and a mono-aromatic hydrocarbon as a desorbent material. CSZ-1 has a composition in terms of mole ratios of oxides of 0.05 to 0.55 cesium and/or thallium: 0.45 to 0.95 Na.sub.2 O:Al.sub.2 O.sub.3 :3 to 7 SiO.sub.2 :XH.sub.2 O, where X is 0 to 10. The CSZ-1 must contain cesium and/or thallium. The mono-aromatic desorbents specifically mentioned are toluene, benzene and diethylbenzene.